A. Field of the Invention
The present invention relates generally to a semiconductor device, and more specifically to a metal-insulator-semiconductor field effect transistor (MISFET) having an oxidized aluminum nitride gate insulator formed on a silicon or gallium nitride semiconductor substrate, and a method of making the same.
B. Discussion of the Related Art
Manufacture of a conventional MIS (metal-insulator-semiconductor)-type semiconductor device involves forming a gate insulator on a semiconductor substrate, and subsequently forming a gate electrode on the gate insulator. Typically, the semiconductor substrate consists of silicon (Si) or gallium arsenide (GaAs), and the gate insulator comprises a film of SiO2, SiN, AlN, or the like, directly deposited on the substrate.
Conventional MISFETs include a silicon dioxide (SiO2) gate insulator deposited on a silicon substrate. However, it is preferable that MISFETs utilize an insulator made from a material other than SiO2, and a substrate made from a material other than silicon. For example, substrates made from a gallium nitride-based compound semiconductors such as, gallium nitride (GaN), gallium aluminum nitride (GaAlN), and indium gallium nitride (InGaN), are preferable since such substrates have direct band gaps in the range of 1.95 eV to 6 eV. For this reason, these compound semiconductors are promising as materials for light-emitting devices such as light-emitting diodes and laser diodes, and for high operating temperature circuits.
Unfortunately, when a silicon dioxide gate insulator is deposited on a gallium nitride substrate or a substrate made from a material other than silicon, the electrical properties of the deposited silicon dioxide gate insulator erode the performance of the conventional MISFET. Thus, a MISFET structure on a GaN substrate is not practical and will have poor performance characteristics.
The reason for this is that the best oxides for use as gate insulators in MISFETs are thermally formed by the chemical reaction of oxygen (O2) gas with the surface of the MISFET substrate. Such native oxides, as they are conventionally called, are not chemically stable for all materials. Further. semiconductor materials that form good FETs and react with oxygen to form a good gate insulator rarely exist. For example, a pure gallium nitride substrate will not react directly with oxygen to form stable oxides. Rather, the gallium nitride reacts with oxygen to form a nitrous oxide (NO) gas and water-soluble Ga2O3.This creates reliability problems because the Ga2O3 will absorb water (H2O) from the ambient environment, changing its electrical behavior. The electrical behavior of the transistor will change too, rendering it unstable and unreliable over time. The unstable transistor will render unstable the circuit incorporating the transistor.
An object of the present invention, therefore, is to provide a MISFET that effectively utilizes a gallium nitride or silicon substrate. A further object of the present invention is to provide a MISFET which forms a stable FET and which is capable of reacting with oxygen to form a good gate insulator.
A still further object of the present invention is to provide a MISFET which permits complex logic circuits to operate at higher temperatures and in harsher environments than conventional silicon-based circuits.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, the invention comprises a metal-insulator-semiconductor type device comprising: one of a silicon or a gallium nitride substrate having source and drain regions formed in an upper surface; an oxidized aluminum nitride layer formed on the upper surface of the substrate and having a plurality of openings formed therein so to expose the source and drain regions of the substrate; and a metal layer formed in the plurality of openings of the oxidized aluminum nitride layer, the metal layer contacting the source and drain regions of the substrate.
According to another aspect, the invention comprises a method for making a metal-insulator-semiconductor type device, comprising the steps of: depositing an aluminum nitride layer on an upper surface of one of a silicon or gallium nitride substrate; oxidizing the aluminum nitride layer to convert the aluminum nitride layer into an oxidized aluminum nitride layer; etching portions of the oxidized aluminum nitride layer to form a plurality of openings exposing regions of the substrate; forming source and drain regions in an upper surface of the substrate corresponding to the exposed regions of the substrate; and forming a metal layer in the plurality of openings of the oxidized aluminum nitride layer, the metal layer contacting the source and drain regions of the substrate.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.